<!DOCTYPE html>
<html>

<head>
  <link rel="help" href="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-type" />
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
  <script src="/resources/testdriver.js"></script>
  <script src="/resources/testdriver-actions.js"></script>
  <script src="/resources/testdriver-vendor.js"></script>
  <script src="/dom/events/scrolling/scroll_support.js"></script>
</head>

<body>
  <style>
    #scroller {
      overflow: scroll;
      height: 500px;
      width: 500px;
      background-color: blue;
      scroll-snap-type: y mandatory;
      position: absolute;
    }

    .snap_point {
      scroll-snap-align: start;
      width: 40%;
      position: relative;
      left: 30%;
    }

    .big {
      height: 1000%;
      background-color: pink;
      border: solid 1px red;
    }

    .small {
      height: 50%;
      background-color: purple;
      border: solid 1px black;
    }
  </style>
  <div id="scroller">
    <div class="big snap_point" id="big_snap_point"></div>
    <div class="small snap_point">
    <button id="scrollerButton">scrollerButton</button>
    </div>
  </div>
  <script>
    promise_test(async(t) => {
      const x = scroller.clientWidth / 2;
      const y = scroller.clientHeight / 2;

      // Scroll all the way down to the smaller snap area which doesn't cover
      // the snapport.
      let scrollend_promise = new Promise((resolve) => {
        scroller.addEventListener("scrollend", resolve);
      });
      scroller.scrollTop = scroller.scrollHeight;
      await scrollend_promise;

      // Scroll up with one press of the arrow-up button.
      scrollend_promise = new Promise((resolve) => {
        scroller.addEventListener("scrollend", resolve);
      });
      const arrowUp = '\uE013';
      await test_driver.send_keys(scrollerButton, arrowUp);

      await scrollend_promise;
      assert_equals(scroller.scrollTop, big_snap_point.offsetHeight - scroller.clientHeight,
          "scroller is snapped to the bottom of the larger snap area, not the top");
    });
  </script>
</body>

</html>